1. Field of the Invention
This invention relates to devices for coupling rotating shafts with parallel misalignment, i.e. shafts that are radially displaced from each other or that move radially during rotation.
2. Prior Art
In many types of rotating machinery, misaligned rotating shafts need to be coupled together. Sometimes the misalignment also changes while the shafts rotate, thus requiring a coupling that can transmit rotational motion while accommodating varying misalignment. In some types of rotating machinery, the rotating shafts are parallel and the misalignment is radial, with the shafts moving radially with respect to each other while they rotate. An example of such machinery is a type of pump referred to as a Moineau pump described in U.S. Pat. Nos. 1,892,217; 2,028,407; 2,483,370; 2,525,265; 2,505,136; and 2,545,626.
Many different coupling devices have been used in the past to couple misaligned rotating shafts. A commonly used device known as a U-joint comprises two "U" shaped members, each attached to one of the shafts, connected by a cross-shaped member through bearings. U-joints are particularly useful when the axes of rotation of the coupled shafts are not parallel, i.e. they exhibit angular misalignment. However, U-joints have the disadvantage that the bearings wear with use and must be replaced.
Another type of flexible coupling also used for shafts that are not parallel has a pair of collars, attached to the shafts, that are coupled together by a flexible member such as a rubber tube or a cylindrical bellows. This type of coupling usually is not suitable to bear axial loads. Neither this type of coupling nor a U-joint is well suited to coupling rotating shafts that have parallel axes of rotation but are radially misaligned or move radially with respect to each other.